The present disclosure relates to a semiconductor device that includes a memory device configured to store information by utilizing a characteristic that a resistance value is changed, and a method of reading information from such a semiconductor device.
In information appliances such as computers and so forth, DRAM (Dynamic Random Access Memory) which is high in density and operates at a high speed is widely used as a random access memory. However, since the DRAM is complicated in manufacturing process in comparison with a general logic circuit LSI (Large Scale Integrated Circuit) and signal processing used in an electronic appliance, the manufacturing cost is increased. In addition, the DRAM is a volatile memory that information is lost when its power source is turned off and it is necessary to frequently perform a refreshing operation, that is, operations of reading out, amplifying again and rewriting again written information (data).
On the other hand, nowadays a non-volatile memory that information is not lost even when its power source is turned off is frequently used. Since such a non-volatile memory is free from execution of the refreshing operation, a reduction in power consumption is expected. Although various types of memory devices are developed as the memory device used in such a non-volatile memory, there is, as one of them, a so-called variable-resistance memory device that stores information utilizing the characteristic that its resistance value is changed (see, for example, K. Aratani, K. Ohba, T. Mizuguchi, S. Yasuda, T. Shiimoto, T. Tsushima, T. Sone, K. Endo, A. Kouchiyama, S. Sasaki, A. Maesaka, N. Yamada, and H. Narisawa, “A Novel Resistance Memory with High Scalability and Nanosecond Switching”, Technical Digest IEDM 2007, 783-786).
Various methods are proposed as a method of reading out information stored in such a variable-resistance memory device. For example, Unexamined Patent Application Publication No. 2003-323791 discloses an information storage unit in which information is read out by applying a bias voltage to a memory device and detecting a current flowing in the memory device with the bias voltage.